Many programming languages and operating systems have dynamically allocated memory. Dynamically allocated memory is usually divided between a “heap” of freely allocated memory and a “stack” that is allocated and deallocated in a last-in-first-out (LIFO) manner. What both of these commonly used paradigms of dynamic memory have in common is that there is a time when the software author or the compiler can “know” that the value of memory that it considers “deallocated” no longer matters. The operating system usually tracks this on a “page” granularity (usually several thousand contiguous memory locations) and can re-use memory for another program if a full page becomes unneeded in the first program.
It is common for a software function to push data onto the stack to save some state, and then pop the data off of the stack. However, after the data is popped off of the stack, the memory locations that were used to implement the stack still contain data that the software may no longer need. The data has “gone out of scope” or has “passed its lifetime”.
In a modern microprocessor, for example, it is likely that the “writes” to memory that the push operation causes have not fully completed. High performance processors execute many operations in parallel at various stages of execution and can bypass data between processors even if the source of the data has not completed. In the current state of the art, the microprocessor would not be aware that the values represented by the writes are no longer needed. Therefore, the microprocessor would spend resources completing the execution of the writes (e.g., by draining write buffers, doing coherency operations, etc.), which serve no value to the software it is executing.